Integrated circuits, including dies, for example, imager dies such as charge-coupled-devices (CCD) and complementary metal oxide semiconductor (CMOS) dies, have commonly been used in photo-imaging applications. Such dies typically contain thousands of pixel cells in a pixel array on a single chip. Pixel cells convert light into an electrical signal that can then be stored and recalled by an electrical device such as, for example, a processor.
Dies are typically packaged and inserted into imaging devices such as, for example, a digital camera. FIG. 1 illustrates a cross-sectional view of one conventional die package 100. The die package 100 includes a die 14 positioned on a substrate 10. The die 14 includes an array of pixels 16. The die 14 typically has a transparent element 18 attached to a surface containing the array of pixels 16 by an adhesive material 24.
In operation, light radiation enters the transparent element 18 of the die package 100. The transparent element 18 filters out IR radiation that can cause color shifts due to cross talk between pixels in the array of pixels 16. Light radiation is then adsorbed, and image signals are created by the array of pixels 16, which converts the photons from light radiation to electrical signals. Wire bonds 13 conduct electrical output signals from the die 14 to wiring on the substrate 10, which, in turn, connects to external circuitry (not shown). The external circuitry may include processing circuits for storing, compressing, manipulating, or displaying an acquired image.
The FIG. 1 die package 100 is formed by placing the die 14 on the substrate 10, applying adhesive material 24 on the periphery of the die 14, and finally placing the transparent element 18 over the die 14. The adhesive material 24 ensures that the transparent element 18 remains attached to the die 14.
While the package illustrated in FIG. 1 works well, the adhesive material 24 often interferes with the array of pixels 16. During the process of attaching the transparent element 18 to the die 14, adhesive material 24 often covers the edge pixels of the array of pixels 16, as illustrated in FIG. 1. As the transparent element 18 is placed over the die 14, capillary action, as well as the force pushing down on the adhesive material 24, may force the adhesive material 24 onto the array of pixels 16, thus interfering with the operation of the die 14. This can lower the yield of packaged products and may affect the performance of packaged products which pass yield tests.
The problem may also be present in packaged dies fabricated to have display pixels, rather than pixels used to receive an image and convert it to electrical signals, resulting in poor visual quality.